U.S. patent number 8,492,928 [Application Number 12/727,181] was granted by the patent office on 2013-07-23 for ac-to-dc conversion.
This patent grant is currently assigned to American Power Conversion Corporation. The grantee listed for this patent is Michael J. Ingemi, Prasad Pyboyina. Invention is credited to Michael J. Ingemi, Prasad Pyboyina.
United States Patent |
8,492,928 |
Pyboyina , et al. |
July 23, 2013 |
AC-to-DC conversion
Abstract
A front-end converter in an uninterruptible power supply system
is described. In an exemplary design, a front-end converter
includes a boost circuit having first and second inputs, positive,
negative, and neutral output nodes, an inductor, AC inputs, a
battery, and first and second devices. The boost circuit is
configured to provide a positive capacitor voltage between the
positive and neutral nodes and to provide a negative capacitor
voltage between the negative and neutral nodes. The first device
selectively couples the inductor to a first AC input or a positive
port of the battery and the second device selectively couples a
negative port of the battery to the second input. The inductor is
coupled to the first input and is shared between an online mode of
the converter and an on-battery mode of the converter. The battery
is coupled through the inductor to the first input during the
on-battery mode.
Inventors: |
Pyboyina; Prasad (N.
Chelmsford, MA), Ingemi; Michael J. (Norwood, MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Pyboyina; Prasad
Ingemi; Michael J. |
N. Chelmsford
Norwood |
MA
MA |
US
US |
|
|
Assignee: |
American Power Conversion
Corporation (West Kingston, RI)
|
Family
ID: |
44646642 |
Appl.
No.: |
12/727,181 |
Filed: |
March 18, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110227418 A1 |
Sep 22, 2011 |
|
Current U.S.
Class: |
307/85; 307/75;
307/64; 307/66 |
Current CPC
Class: |
H02J
9/062 (20130101); H02M 3/158 (20130101); H02M
1/0085 (20210501) |
Current International
Class: |
H02J
9/00 (20060101); H02J 1/00 (20060101) |
Field of
Search: |
;307/64-66,75,85 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Xu, David M., Yang, C., Kong, J.H., Qian, Zhaoming, "Quasi
Soft-Switching Partly Decoupled Three-Phase PFC With Approximate
Unity Power Factor", IEEE, Institute of Power Electronics, 1998,
pp. 953-957, 0-7803-4340-9/98, Zhejiang University, Hang Zhou,
P.R.C. cited by applicant .
International Search Report and Written Opinion for
PCT/US2011/029053, mailed Oct. 12, 2011. cited by
applicant.
|
Primary Examiner: Amrany; Adi
Attorney, Agent or Firm: Gilman Clark Hunter & Messina
LLC
Claims
What is claimed is:
1. In an uninterruptible power supply (UPS) system, a front-end
converter comprising: a boost circuit having first and second
inputs; a positive output node, a negative output node, and a
neutral output node; and first and second switches, the boost
circuit including directional circuit components comprising first
and second output diodes and first and second input diodes, with an
anode of the first input diode and a cathode of the second input
diode connected to the first input of the boost circuit and an
anode of the second input diode connected to the second input of
the boost circuit, wherein the directional circuit components are
configured to rectify incoming alternating-current (AC) power to
provide a positive voltage across a positive capacitor coupled
between the positive output node and the neutral output node and to
provide a negative voltage across a negative capacitor coupled
between the negative output node and the neutral output node
wherein the first and second inputs are each directly connected to
at least one of the directional circuit components; and wherein an
anode of the first output diode is connected to a cathode of the
first input diode, a cathode of the second output diode is
connected to the anode of the second input diode, the first switch
is connected on one end between the first input diode and the first
output diode and on another end to a neutral connection, and the
second switch is connected on one end between the second output
diode and the second input diode and on another end to the neutral
connection; a single inductor coupled to the first input of the
boost circuit; a first AC input and a neutral AC input together
configured to receive alternating-current power; a battery having a
negative port and a positive port; a first device coupled,
disposed, and configured to selectively couple the single inductor
to one of the first AC input or the positive port of the battery; a
second device coupled, disposed, and configured to selectively
couple the negative port of the battery to the second input of the
boost circuit; a third device coupled to the anode of the first
input diode and the cathode of the first input diode and configured
to selectively bypass the first input diode; and a first controller
coupled to the third device and configured to cause the third
device to close to bypass the first input diode during an
on-battery mode and to open during an online mode, wherein the
single inductor is shared between the online mode of the converter
and the on-battery mode of the converter and the battery is coupled
through the single inductor to the first input of the boost circuit
during the on-battery mode; and wherein the single inductor is an
only inductor coupling the battery to the boost circuit.
2. The converter of claim 1 further comprising a single current
transformer coupled in series with the single inductor between the
first device and the first input of the boost circuit.
3. The converter of claim 2 comprising a second controller coupled
to the single current transformer, the positive output node, the
negative output node, and the first and second switches, the second
controller being configured to couple to an output of an inverter
to be coupled to the positive and negative output nodes, wherein
the second controller is configured to: cause, during a positive
half cycle of a voltage at the output of the inverter, the second
switch to close and the first switch to open and close in order to
maintain a voltage at the positive output node within a first
desired range; and cause, during a negative half cycle of a voltage
at the output of the inverter, the first switch to close and the
second switch to open and close in order to maintain a voltage at
the negative output node within a second desired range.
4. The converter of claim 1 further comprising a second controller
coupled to the first and second devices and configured to: cause
the first device to couple the single inductor to the AC input
during the online mode of the converter and to couple the single
inductor to the positive port of the battery during the on-battery
mode of the converter; and cause the second device to couple the
negative port of the battery to the neutral output node during the
online mode of the converter and to couple the negative port of the
battery to the second input of the boost circuit during the
on-battery mode of the converter.
5. The converter of claim 1 wherein the second device is configured
to selectively couple the negative port of the battery to one of
the second input of the boost circuit or to the negative output
node.
6. The converter of claim 1 wherein the first and second devices
are relays.
7. The converter of claim 1 comprising: a DC-AC inverter coupled to
the positive output node, the negative output node, and the neutral
output node, and including a positive DC inverter output and a
neutral DC inverter output.
8. In an uninterruptible power supply (UPS) system, a front-end
converter comprising: a boost circuit having first and second
inputs, a positive output node, a negative output node, and a
neutral output node, the boost circuit configured to rectify
incoming alternating-current (AC) power to provide a positive
voltage across a positive capacitor coupled between the positive
output node and the neutral output node and to provide a negative
voltage across a negative capacitor coupled between the negative
output node and the neutral output node; a first inductor coupled
to the first input of the boost circuit; a first AC input and a
neutral AC input together configured to receive alternating-current
power; a battery having a negative port and a positive port; a
first device coupled, disposed, and configured to selectively
couple the first single inductor to one of the first AC input or
the positive port of the battery; and a second device coupled,
disposed, and configured to selectively couple the negative port of
the battery to the second input of the boost circuit; wherein the
first inductor is shared between an online mode of the converter
and an on-battery mode of the converter and the battery is coupled
through the first inductor to the first input of the boost circuit
during the on-battery mode and further wherein the first AC input
is configured to couple to a first phase port of a three-phase AC
source, the front-end converter further comprising: a second AC
input configured to couple to a second phase port of the
three-phase AC source; a third AC input configured to couple to a
third phase port of the three-phase AC source; a second inductor
coupled between the second device and the second input of the boost
circuit, the second device being configured to selectively couple
the second single inductor to one of the negative port of the
battery or to the second AC input; a fourth device; and a third
inductor coupled between the fourth device and a third input of the
boost circuit, the fourth device being configured to selectively
couple the third inductor to the third AC input.
9. The converter of claim 8 wherein the boost circuit comprises:
first and second input diodes, with, an anode of the first input
diode and a cathode of the second input diode connected to the
first input of the boost circuit and an anode of the second input
diode connected to the neutral AC input; third and fourth input
diodes, with an anode of the third input diode and a cathode of the
fourth input diode connected to the second input of the boost
circuit and an anode of the fourth input diode connected to the
neutral AC input; and fifth and sixth input diodes, with an anode
of the fifth input diode and a cathode of the sixth input diode
connected to the third input of the boost circuit and an anode of
the sixth input diode connected to the neutral AC input; the
converter further comprising: a fifth device coupled to an anode of
the fourth input diode and a cathode of the fourth input diode and
configured to selectively bypass the fourth input diode; and a
controller coupled to the fifth device and configured to cause the
fifth device to close to bypass the fourth input diode during the
on-battery mode and to open during the online mode.
10. The converter of claim 9 further comprising a third device
coupled to the anode of the first input diode and a cathode of the
first input diode and configured to selectively bypass the first
input diode, the controller being coupled to the third device and
configured to cause the third device to close to bypass the first
input diode during the on-battery mode and to open during the
online mode.
11. The converter of claim 8 wherein the boost circuit comprises:
first and second input diodes, with an anode of the first input
diode and a cathode of the second input diode connected to the
first input of the boost circuit and an anode of the second input
diode connected to the neutral AC input; third and fourth input
diodes, with an anode of the third input diode and a cathode of the
fourth input diode connected to the second input of the boost
circuit and an anode of the fourth input diode connected to the
neutral AC input; and fifth and sixth input diodes, with an anode
of the fifth input diode and a cathode of the sixth input diode
connected to the third input of the boost circuit and an anode of
the sixth input diode connected to the neutral AC input; the
converter further comprising: a first current transformer coupled
between cathodes of the first, third, and fifth input diodes and an
anode of a positive output diode of the boost circuit; and a second
current transformer coupled between anodes of the second, fourth,
and sixth input diodes and a cathode of a negative output diode of
the boost circuit.
12. The converter of claim 8 further comprising: a positive half
cycle battery switch coupled, disposed, and configured to
selectively couple the positive port of the battery to the neutral
output node; a negative half cycle battery switch coupled,
disposed, and configured to selectively couple the negative port of
the battery to the neutral output node; and a controller coupled to
the positive and negative half cycle battery switches and
configured to cause the positive half cycle switch to be open,
isolating the positive port of the battery from the neutral output
node, and the negative half cycle switch to be closed, coupling the
negative port of the battery to the neutral output node, during a
positive half cycle of an inverter output voltage, and to cause the
positive half cycle switch to be closed, coupling the positive port
of the battery to the neutral output node, and the negative half
cycle switch to be open, isolating the negative port of the battery
from the neutral output node, during a negative half cycle of the
inverter output voltage.
13. An uninterruptible power supply (UPS) comprising: a DC-DC
front-end converter including: a plurality of converter inputs
configured to be coupled to a three phase AC power source; a
positive DC front-end output; a negative DC front-end output; and a
neutral front-end output; a positive capacitor coupled between the
positive DC front-end output and the neutral front-end output; a
negative capacitor coupled between the negative DC front-end output
and the neutral front-end output; and a DC-AC inverter coupled to
the positive DC front-end output, the negative DC front-end output,
and the neutral front-end output, and including a positive DC
inverter output and a neutral DC inverter output; the DC-DC
front-end converter further including: a boost circuit; a battery;
a single first inductor coupled between a first input of the boost
circuit and a first device configured to selectively couple the
single first inductor to a positive port of the battery or to a
first of the converter inputs; a single second inductor coupled
between a second input of the boost circuit and a second device
configured to selectively couple the single second inductor to a
negative port of the battery or to a second of the converter
inputs; and a single third inductor coupled between a third input
of the boost circuit and a third device configured to selectively
couple the single third inductor to a third of the converter
inputs.
14. The UPS of claim 13 wherein the converter further includes
fourth and fifth devices configured to bypass first and second
input diodes during an on-battery mode of the converter.
15. The UPS of claim 14 wherein the converter further includes: a
sixth device configured to selectively couple the positive port of
the battery to a neutral node of the converter; and a seventh
device configured to selectively couple the negative port of the
battery to the neutral node of the converter.
16. The UPS of claim 15 wherein the converter further includes a
controller coupled to the fourth, fifth, sixth, and seventh devices
and configured to cause: the fourth and fifth devices to be closed,
bypassing the first and second input devices, during the on-battery
mode of the converter; the sixth device to be open, isolating the
positive port of the battery from the neutral node, and the seventh
device to be closed, connecting the negative port of the battery to
the neutral node, during a positive half cycle of an output voltage
of the inverter; and the sixth device to be closed, connecting the
positive port of the battery to the neutral node, and the seventh
device to be open, isolating the negative port of the battery from
the neutral node, during a negative half cycle of the output
voltage of the inverter.
Description
BACKGROUND
Companies and individuals rely on having a consistent supply of
power to electronic devices more than ever before. Without power,
companies may be unable to manufacture goods, or to operate at all,
such as if the company is in the business of supplying information
over the Internet. Without power, businesses and individuals may be
completely incapacitated regarding critical activities, such as
designing products, making goods, providing services, and
transacting personal finances (e.g., filing tax returns, and paying
bills). Uninterruptible power supplies (UPSs) are often used to
provide backup power in case of a power outage. UPSs are commonly
used on computing equipment to guard against data being lost due to
a power outage before the data are saved. UPSs used with computing
equipment also help to guard against a loss in service by providers
of information over the Internet, such as by servers, e.g., hosting
web pages.
Online UPS systems typically contain a boost stage power factor
correction (PFC) front-end converter 502 and an inverter stage rear
end 504 as shown in FIG. 1 for the UPS system 500. The inputs to
the front-end converter are a 60/50 HZ AC supply 506 and Battery DC
supply 508. The UPS 500 works in two modes of operation based on
the input voltage. When the input AC voltage is within an
acceptable range for the boost converter 502 to operate on the AC
supply voltage, the UPS 500 works in an online mode. In this mode,
the front-end boost converter 502 takes input power from AC supply
506 and converters the voltage to two DC voltages and provides
these voltages to two DC busses 510, 512, with a positive DC bus
voltage (+DC) and a negative dc bus voltage (-DC), respectively.
When the input AC voltage is not available or not within the
acceptable range, the UPS works in an on-battery mode. In this
mode, the front-end boost converter 502 takes DC input power from
the battery 508 and produces positive and negative DC bus voltages
and delivers these voltages to the respective busses 510, 512.
A central control system (controller, not shown) in the UPS system
500 monitors the input AC voltage and controls transfers between
the two different modes. Traditionally, relays have been used to
transfer the front-end boost converter inputs from AC supply to DC
supply and vice versa. Recently, Silicone Controlled Rectifiers
(SCRs) have been used for this purpose.
Two bulk capacitors 514, 516 are provided between the DC busses
510, 512. The capacitors 514, 516 are part, of the front end
converter 502, but shown outside the converter 502 for illustrative
purposes. The capacitors 514, 516 provide energy to a load through
the inverter 504 during transfers between different modes of the
UPS 500 to help ensure transfers without significant voltage drops
to the load.
The inverter 504 is a DC-AC converter that takes input from the
positive and negative DC bus voltages and produces an AC voltage at
the output. The inverter 504 in typical online UPS systems
comprises two buck converters that are controlled by pulse width
modulation (PWM) controllers to provide a desired sine wave
output.
Referring to FIG. 2, with further reference to FIG. 1, a positive
buck converter 522 converts DC voltage from the +DC bus 510 to AC
voltage during positive half cycles of the output voltage and a
negative buck converter 524 converts DC voltage from the -DC bus
512 to AC voltage during negative half cycles of the output
voltage. The outputs of both of the buck converters 522, 524 are
combined to get a full cycle of AC voltage. In other words, load
power is supplied from the +DC bus 510 during positive half cycles
of the output (load) voltage and load power is supplied from the
-DC bus 512 during negative half cycles of the output voltage.
Power Factor Correction of Online UPS Systems
There are two modes of front-end boost operation in online UPS
systems, online mode and on-battery mode.
Online Mode
Referring to FIG. 3, with further reference to FIGS. 1-2, in online
mode the front-end converter 502 uses a positive boost converter
526 and a negative boost converter 528. The front-end converter 502
takes input from the AC supply 506 and outputs two DC voltages. The
front-end converter 502 works as a PFC converter while it is
working from AC input voltage. The positive boost converter 526
converts positive half cycles of AC input voltage to DC voltage
during the positive half cycles of the input voltage. This positive
output is given to the +DC bus capacitor 514. The negative boost
converter 528 converts negative half cycles of AC input voltage to
DC voltage during the negative half cycles of the input voltage.
This negative output is given to the -DC bus capacitor 516.
Even though the front-end converter 502 uses two converters 526,
528 to supply power to the two DC buses 510, 512, some of the
components (e.g., inductors and current transformers) can be shared
so these can be common components for both positive and negative
boost converters 526, 528.
FIGS. 4-6 show three circuits 550, 560, and 570 for implementing
PFC from an AC supply. The circuits 550, 560, 570 contain positive
converters 552, 562, 572 and negative converters 554, 564, 574. The
circuit in Black is used in both positive and negative half cycles.
These methods are well discussed in the literature. The number of
components are not the same for all three topologies. The selection
of the topology (circuit) depends on several factors such as power
level, control architecture, etc. Of the three circuits 550, 560,
570, the circuit 550 offers several advantages at lower power
levels such, as high, efficiency, low cost, simple control
implementation and lower part count.
On-Battery Mode
Referring to FIG. 7, with further reference to FIG. 1, in the
on-battery mode of operation, the front-end converter 502 takes
input power from the battery 508 as the voltage source and delivers
power to both the positive and negative DC buses 510, 512. The
battery 508 can be connected in different configurations, such as
positive non-floating, negative non-floating, or floating. The
battery 508 provides positive non-floating voltage when the
battery's negative terminal is connected to the neutral and
provides negative non-floating voltage when the battery's positive
terminal is connected to the neutral. In floating configuration,
neither of the battery's terminals is net connected to neutral. The
non-floating battery (one terminal of the battery is connected to
neutral) simplifies battery voltage sensing and also simplifies the
charger control.
Power conversion implementation techniques are different for
floating and non-floating batteries in PFC. Known implementations
are using boost and buck-boost converters for non-floating battery
systems as shown in FIG. 7, and using twin boost converters for
floating battery systems as shown in FIG. 9.
Boost and Buck-Boost Converters
As discussed above, one DC voltage from the battery 508 is used to
derive two DC output voltages with different polarities. A boost
converter 580 is used to boost the battery voltage to the DC bus
voltage with the same polarity as the battery 508. The boost
converter operation is discussed in above in online mode of
operation. A buck-boost converter 590 may be used to derive a DC
voltage from the battery 508 with a polarity opposite that of the
battery 508.
Referring to FIG. 8, the buck-boost converter 590 includes a buck
portion 592 and a boost portion 594. The buck portion 592 includes
a switch 596 and an inductor 598, and, the boost portion 594
includes the inductor 598, and a diode 600. When the switch 596 is
ON (closed), current flowing through the inductor 598 increases and
stores energy. When the switch 596 is OFF (open), the stored energy
in the inductor 598 is transferred to the capacitor 516. Thus,
while the switch 598 is ON the current path is through the battery
508, the switch 596, and the inductor 598, and while the switch 596
is OFF the current path is through the inductor 598, the capacitor
516, and the diode 600. For a battery with a voltage between 120
VDC and 240 VDC and an output bus voltage of +400 volts, the switch
596 should be rated at 1200V as the switch 596 switches the battery
voltage plus the +DC bus voltage. Also, the diode 600 should be
rated at 1200V.
The total front-end converter 502 uses two converters (boost 580
and buck-boost 590) to transfer energy from the battery 508 to the
positive and negative DC buses 510, 512. The converters 580, 590
are separate converters and do not share components during
on-battery operation. Because the two converters 580, 590 are
separate and operate concurrently, for improved efficiency, in
on-battery operation, single inductor solutions shown in FIGS. 4
and 5 can not be implemented.
Twin Boost Converters
Another approach to output both positive and negative voltages from
a single battery is by using a floating battery and a twin boost
converters configuration 610 as shown in FIG. 9. In this
configuration, neither of the battery terminals is connected to the
neutral, unlike the buck-boost approach. Operation of the twin
boost converter is discussed in U.S. Pat. No. 5,654,591.
Three-Phase Applications
Prior three-phase front-end topologies typically have used fully
decoupled PFCs, while some have used partially-decoupled PFCs at
lower power levels because of a fewer CTs and better utilization of
silicon and magnetics. For example, a three-phase,
partially-decoupled PFC is discussed in U.S. Pat. No. 7,005,759, in
which four inductors are used to implement three-phase front-end
converter in an online system. Referring to FIG. 10, which is FIG.
3 in U.S. Pat. No. 7,005,759, a three-phase front-end converter 620
includes a switch S.sub.o that is open during the online operation
so that the PFC can work from input AC through inductors L.sub.a,
L.sub.b, and L.sub.c and diodes D.sub.1 to D.sub.6. The inductors
L.sub.a, L.sub.b, L.sub.c are boost inductors for the three-phase
PFC. A description of PFC operation can be found in
"Quasi-Soft-Switching Partly Decoupled Threephase PFC. With
Approximate Unity Power Factor" by David M. XU C. Yang J. H. Kong
Zhaoming. Qian (IEEE, 1998). During the on-battery operation, the
switch S.sub.o is closed and the battery supplies the power to the
dc buses. The inductor L is used as boost inductor in the
on-battery mode of operation. CTs are not shown but would be
disposed between L.sub.a and D.sub.1, L.sub.b and D.sub.2, L.sub.c
and D.sub.3, and between the battery and L.
SUMMARY
An example of a front-end converter in an uninterruptible power
supply (UPS) system includes: a boost circuit having first and
second inputs, a positive output node, a negative output node, and
a neutral output node, the boost circuit configured to rectify
incoming alternating-current (AC) power to provide a positive
voltage across a positive capacitor coupled between the positive
node and the neutral node and to provide a negative voltage across
a negative capacitor coupled between the negative node and the
neutral node; an inductor coupled to the first input of the boost
circuit; a first AC input and a neutral AC input together
configured to receive alternating-current power; a battery having a
negative port and a positive port; a first device coupled,
disposed, and configured to selectively couple the inductor to one
of the first AC input or the positive port of the battery; and a
second device coupled, disposed, and configured to selectively
couple the negative port of the battery to the second input of the
boost circuit; where the inductor is shared between an online mode
of the converter and an on-battery mode of the converter and the
battery is coupled through the inductor to the first input of the
boost circuit during the on-battery mode.
Implementations of such a front-end converter may include one or
more of the following features. The converter further includes a
single current transformer coupled in series with the inductor
between the first device and the first input of the boost circuit.
The boost circuit includes first and second switches, and the
converter further includes a single controller coupled to the
single current transformer, the positive output node, the negative
output node, and the first and second switches, the single
controller being configured to couple to an output of an inverter
to be coupled to the positive and negative nodes, where the single
controller is configured to: cause, during a positive half cycle of
a voltage at the output of the inverter, the second switch to close
and the first switch to open and close in order to maintain a
voltage at the positive output node within a first desired range;
and cause, during a negative half cycle of a voltage at the output
of the inverter, the first switch to close and the second switch
to, open and close in order to maintain a voltage at the negative
output node within a second desired range. The converter further
includes a single controller coupled to the first and second
devices and configured to: cause the first device to couple the
inductor to the AC input during the online mode of the converter
and to couple the inductor to the positive port of the battery
during the on-battery mode of the converter; and cause the second
device to couple the negative port of the battery to the neutral
node during the online mode of the converter and to couple the
negative port of the battery to the second input of the boost
circuit during the on-battery mode of the converter.
Additionally or alternatively, implementations of the front-end
converter may include one or more of the following features. The
boost circuit includes: first and second input diodes, with an
anode of the first input diode and a cathode of the second input
diode connected to the first input of the boost circuit and an
anode of the second input diode connected to the second input of
the boost circuit; first and second output diodes; and first and
second switches; where an anode of the first output diode is
connected to a cathode of the first input diode, a cathode of the
second output diode is connected to an anode of the second input
diode, the first switch is connected on one end between the first
input diode and the first output diode and on another end to a
neutral connection, and the second switch is connected on one end
between the second output diode and the second input diode and on
another end to the neutral connection. The converter further
includes: a third device coupled to the anode of the first input
diode and a cathode of the first input diode and configured to
selectively bypass the first input diode; and a controller coupled
to the third device and configured to cause the third device to
close to bypass the first input diode during the on-battery mode
and to open during the online mode.
Additionally or alternatively, implementations of the front-end
converter may include one or more of the following features. The
second device is configured to selectively couple the negative port
of the battery to one of the second input of the boost circuit or
to the negative node. The inductor is a first inductor and the
first AC input is configured to couple to a first phase port of a
three-phase AC source, the converter further including: a second AC
input configured to couple to a second phase port of the
three-phase AC source; a third AC input configured to couple to a
third phase port of the three-phase AC source; a second inductor
coupled between the second device and the second input of the boost
circuit, the second device being configured to selectively couple
the second inductor to one of the negative port of the battery or
to the second AC input; a fourth device; and a third inductor
coupled between the fourth device and a third input of the boost
circuit, the fourth device being configured to selectively couple
the third inductor to the third AC input. The boost circuit
includes: first and second input diodes, with an anode of the first
input diode and a cathode of the second input diode connected to
the first input of the boost circuit and an anode of the second
input diode connected to the neutral AC input; third and fourth
input diodes, with an, anode of the third input diode and a cathode
of the fourth input diode connected to the second input of the
boost circuit and an anode of the fourth input diode connected to
the neutral AC input; and fifth and sixth input diodes, with an
anode of the fifth input diode and a cathode of the sixth input
diode connected to the third input of the boost circuit and an
anode of the sixth input diode connected to the neutral AC input;
the converter further including: a fifth device coupled to an anode
of the fourth input diode and a cathode of the fourth input diode
and configured to selectively bypass the fourth input diode; and a
controller coupled to the fifth device and configured to cause the
fifth device to close to bypass the fourth input diode during the
on-battery mode and to open during the online mode. The converter
further includes a third device coupled to the anode of the first
input diode and a cathode of the first input diode and configured
to selectively bypass the first input diode, the controller being
coupled to the third device and configured to cause the third
device to close to bypass the first input diode during the
on-battery mode and to open during the online mode. The boost
circuit includes: first and second input diodes, with an anode of
the first input diode and a cathode of the second input diode
connected to the first input of the boost circuit and an anode of
the second input diode connected to the neutral AC input; third and
fourth input diodes, with an anode of the third input diode and a
cathode of the fourth input diode connected to the second input of
the boost circuit and an anode of the fourth input diode connected
to the neutral AC input; and fifth and sixth input diodes, with an
anode of the fifth input diode and a cathode of the sixth input
diode connected to the third input of the boost circuit and an
anode of the sixth input diode connected to the neutral AC input;
the converter further including: a first current transformer
coupled between cathodes of the first, third, and fifth input
diodes and an anode of a positive output diode of the boost
circuit; and a second current transformer coupled between anodes of
the second, fourth, and sixth input diodes and a cathode of a
negative output diode of the boost circuit. The converter further
includes: a positive half cycle battery switch coupled, disposed,
and configured to selectively couple the positive port of the
battery to the neutral node; a negative half cycle battery switch
coupled, disposed, and configured to selectively couple the
negative port of the battery to the neutral node; and a controller
coupled to the positive and negative half cycle battery switches
and configured to cause the positive half cycle switch to be open,
isolating the positive port of the battery from the neutral node,
and the negative half cycle switch to be closed, coupling the
negative port of the battery to the neutral node, during a positive
half cycle of an inverter output voltage, and to cause the positive
half cycle switch to be closed, coupling the positive port of the
battery to the neutral node, and the negative half cycle switch to
be open, isolating the negative port of the battery from the
neutral node, during a negative half cycle of the inverter output
voltage. The first and second devices are relays.
An example of an uninterruptible power supply (UPS) includes: a
DC-DC front-end converter including: converter inputs configured to
be coupled to an AC power supply; a positive DC front-end output; a
negative DC front-end output; and a neutral front-end output; the
UPS further including a positive capacitor coupled between the
positive DC front-end output and the neutral front-end output; a
negative capacitor coupled between the negative DC front-end output
and the neutral front-end output; and a DC-AC inverter coupled to
the positive DC front-end output, the negative DC front-end output,
and the neutral front-end output, and including a positive DC
inverter output and a neutral DC inverter output; the DC-DC
front-end converter further including: a boost circuit; a battery;
and a single inductor coupled between an input of the boost circuit
and a device configured to selectively couple the inductor to a
positive port of the battery or to a first of the converter
inputs.
Implementations of such a UPS may include one or more of the
following features. The DC-DC front-end converter is configured to
bypass a diode of the converter during an on-battery mode of the
converter. The DC-DC front-end converter further includes a single
current transformer coupled between the device and the input of the
boost circuit. The converter inputs are configured to be coupled to
a three-phase AC power source, the single inductor is a single
first inductor; the device is a first device, and the input of the
boost circuit is a first input of the boost circuit, the DC-DC
front-end converter further including: a single second inductor
coupled between a second input of the boost circuit and a second
device configured to selectively couple the second inductor to a
negative port of the battery or to a second of the converter
inputs; and a single third inductor coupled between a third input
of the boost circuit and a third device configured to selectively
couple the third inductor to a third of the converter inputs. The
converter further includes fourth and fifth devices configured to
bypass first and second input diodes during an on-battery mode of
the converter. The converter further includes: a sixth device
configured to selectively couple the positive port of the battery
to a neutral node of the converter; and a seventh device configured
to selectively couple the negative port of the battery to the
neutral node of the converter. The converter further includes a
controller coupled to the fourth, fifth, sixth, and seventh devices
and configured to cause: the fourth and fifth devices to be closed,
bypassing the first and second input devices, during the on-battery
mode of the converter; the sixth device to be open, isolating the
positive port of the battery from the neutral node, and the seventh
device to be closed, connecting the negative port of the battery to
the neutral node, during a positive half cycle of an output voltage
of the inverter; and the sixth device to be closed, connecting the
positive port of the battery to the neutral node, and the seventh
device to be open, isolating the negative port of the battery from
the neutral node, during a negative half cycle of the output
voltage of the inverter.
Items and/or techniques described herein may provide one or more of
the following capabilities. For example, front-end converters with
reduced components may provide lower cost of the total circuit,
high efficiency, and simplified control implementation. Lower-rated
components may be used in converters, e.g., 600V rated components
of a 230V system as opposed to 1200V rated components. Efficiency
of converters may be improved. Front-end converters with a single
inductor, a single current transformer, and a single controller may
be used, reducing a quantity of analog-to-digital conversion
channels and reducing cost. Front-end converters may be used that
contain no SCRs, yielding improved efficiency, less or no heat
sinking, and reduced cost compared to converters with SCRs.
Front-end converters may use batteries in floating voltage
configurations during online operation, simplifying charger control
circuitry. Printed circuit board space used by front-end converters
may be reduced and power density increased.
While pairs of items/techniques and corresponding effects have been
described, it may be possible for a noted effect to be achieved by
means other than those noted, and a noted item/technique may not
necessarily yield the noted effect.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an online UPS system.
FIG. 2 is a block diagram of an inverter without a transformer in
an online UPS system.
FIG. 3 is a block diagram of a single-phase power factor correction
circuit in an online mode.
FIGS. 4-6 are circuit diagrams of front-end boost converters for
implementing PFC from an AC supply.
FIG. 7 is a circuit diagram of front-end converter operation in an
on-battery mode of an online UPS.
FIG. 8 is a circuit diagram of a typical buck-boost converter
circuit.
FIG. 9 is a circuit diagram of a twin boost topology.
FIG. 10 is a circuit diagram of a three-phase front-end
converter.
FIG. 11 is a circuit diagram of a shared-component front-end
converter in an online mode during a positive half cycle of input
voltage.
FIG. 12 is a circuit diagram of the shared-component front-end
converter in the online mode during a negative half cycle of input
voltage.
FIG. 13 is a circuit, diagram of the shared-component front-end
converter in an on-battery mode.
FIG. 14 is a time plot of switch states and currents relative to an
output voltage cycle of the converter shown in FIG. 10 in the
on-battery mode.
FIG. 15 is a circuit diagram of an alternative shared-component
front-end converter in an online mode.
FIG. 16 is a circuit diagram of a shared-component three-phase
front-end converter in an on-battery mode during a positive half
cycle of an inverter output voltage.
FIG. 17 is a circuit diagram of the shared-component three-phase
front-end converter shown in FIG. 16 in the on-battery mode during
a negative half cycle of the inverter output voltage.
FIG. 18 is an alternative circuit diagram of a shared-component
three-phase front-end converter in an on-battery mode during a
positive half cycle of an inverter output voltage.
FIG. 19 is a circuit diagram of the shared-component three-phase
front-end converter shown in FIG. 18 in the on-battery mode during
a negative half cycle of the inverter output voltage.
DETAILED DESCRIPTION
The disclosure provided herein describes, among other things,
techniques, embodied in methods and/or apparatus, for providing
front-end, converters, e.g., for UPSs containing front-end AC-DC
converters connected to DC-AC inverters. For example, front-end
converters with shared components for both online and on-battery
operation, and with the battery connected in a floating voltage
configuration, are provided. Devices, preferably relays,
selectively connect the front-end converter to an AC source during
online operation, and connect a battery to the converter during
on-battery operation. A single inductor is shared between the
online and on-battery modes, coupling either the AC source or the
battery to a boost circuit. A three-phase front-end converter uses
devices, preferably relays, to connect each input phase to a boost
circuit via a single inductor. The single inductor for each of two
of the phases is shared between online and on-battery modes. Bypass
mechanisms are preferably used to bypass input diodes of the boost
circuit during on-battery mode. Further, either a positive or
negative port of a battery can be selectively connected to the
converter, and the other port to neutral, depending upon a half
cycle of an inverter output voltage. Other embodiments are within
the scope of the disclosure.
Single-Phase Circuitry
Referring to FIG. 11, a shared-component, single-phase, front-end
converter 10 includes relays 12, 14, a battery 16, an inductor 18,
a current transformer (CT) 20, a controller 22, diodes 24, 26, 28,
30, and switches 32, 34. The converter 10 is connected at its input
to an AC power source 40 and at its output to positive and negative
bus capacitors 36, 38, respectively. The converter 10 can operate
from AC supply as well as the battery 16 (DC voltage) with a
reduced number of components. The converter 10 is preferably,
though not necessarily, designed to be a 230V system, i.e., the
battery 16 provides 230VDC and the converter can be connected to a
230VAC source 40. The components of the converter 10 are preferably
rated at about 600V or less. The converter 10 uses no SCRs, and as
described below, the battery 16 is connected to neutral during
online operation. The converter 10 is preferably connected to an
inverter as shown in FIG. 1. Thus, an inverter and an output of the
inverter is referred to below although not shown in FIG. 11.
The controller 22 is coupled and configured to monitor conditions
and, affect states of components of the converter 10. The
controller 22 is connected to the CT 20 to receive indications of
the current through the CT. The controller 22 is also connected to
nodes 50 and 52 to monitor DC voltages at the capacitors 36, 38.
The controller 22 is also connected to the switches 32, 34 to
control the switches 32, 34 to open (not conduct) or close
(conduct) as desired. The controller 22 coordinates transitions
between online and on-battery mode due to one or more relevant
conditions, e.g., overvoltage of the AC source, blackouts, voltage
spikes, return of AC source voltage to desired conditions, etc.
Alternatively, the controller 22 may receive indications of
transitions by a separate controller that coordinates the
transitions, e.g., determines that a transition condition has
occurred and instructs/initiates the transition.
The inductor 18 and the CT 20 are shared by both online, and
on-battery modes. The relay 12 is coupled and configured to
selectively connect the inductor 18 to either the AC source 40 or
the positive terminal of the battery 16. The inductor 18 is
connected through the CT 20 to positive and negative boost
converters. The inductor 18 is the only inductor in the converter
10. Thus, the converter 10 includes only a single inductor. Here, a
"single" inductor is a single inductance in the circuit location
shown, but the inductance may be made up of multiple physical
devices. The relay 14 is configured and coupled to selectively
connect the battery's negative terminal to either neutral
(connected to the AC source 40), or to the diode 26, the switch 34,
and the diode 30.
In online mode, the relays 12, 14 are connected to normally-open
(NO) positions and the front-end converter 10 works from input AC
voltage from the AC source 40. During the positive half cycle of
the input voltage, a positive boost converter portion comprising
the inductor 18, the CT 20, the controller 22, the diodes 24, 28,
and the switch 32 converts the input positive AC half-cycle voltage
to a DC voltage and provides this voltage to the capacitor 36.
During the positive half cycle, the controller 22 may open the
boost switch 34 and monitors the voltage at the positive DC bus
capacitor 36 and the current through the CT 20. Based on the
monitored voltage and current, the controller 22 opens and closes
the boost switch 32 to maintain the voltage at the capacitor 36 at
about a desired level, e.g., within a desired voltage range. A line
42 shows the current path while the boost switch 32 is turned on
(closed/conducting) and a line 44 shows the current path while the
boost switch 32 is off (open/non-conducting).
Referring to FIG. 12, during the negative half cycle, the
controller 22 may open the boost switch 32 and monitors the voltage
at the negative DC bus capacitor 38 and the current through the CT
20. Based on the monitored voltage and current, the controller 22
opens and closes the boost switch 34 to maintain the voltage at the
capacitor 38 at about a desired level, e.g., within a desired
voltage range. A line 46 shows the current path while the boost
switch 34 is turned on (closed/conducting) and a line 48 shows the
current path while the boost switch 34 is off
(open/non-conducting).
During both the positive and negative half cycles of the source 40,
the inductor 18 and the CT 20 carry current. Conversely, the diodes
24, 26, 28, 30, the switches 32, 34, and the capacitors 36, 38 each
conduct current during only respective half cycles of the input
voltage source 40.
Referring to FIG. 13, with further reference to FIG. 11, in the
on-battery mode the relays 12, 14 are connected to their
normally-closed (NC) positions and the front-end converter 10 works
from the DC voltage of the battery 16 and is isolated from the AC
voltage source 40. The controller 22 controls the front-end
converter 10 during on-battery operation in sync with the output
voltage of an inverter (not shown) connected to the converter 10
across nodes 50, 52, as opposed to being in sync with the input
voltage during online operation. As described below, the switches
32, 34 are each closed completely for one half cycle of the output
voltage and are opened and closed as desired in the other half
cycle of the output voltage. Further, as discussed above and below,
only the single inductor 18 is used in the converter 10 for both
positive and negative half cycles of the input when the converter
10 is running in online mode, and for both positive and negative
half cycles of the output voltage when the converter 10 is running
in on-battery mode. Also, only the single current transformer 20
and the single controller 22 can be used to operate the converter
10 during both online and on-battery operation, as the relay 14 is
configured and coupled to selectively connect the battery's
negative terminal to either neutral or to the diode 26, the switch
34, and the diode 30.
During the positive half cycle of the output voltage, the
controller 22 closes the switch 34 and opens and closes the switch
32 as desired. The controller 22 monitors the current through the
CT 20 and the voltage at node 50, determines a pulse width
modulation (PWM) rate using the monitored current and voltage, and
opens and closes the switch 32 in accordance with the determined
PWM rate to maintain the voltage at the node 50 at about a desired
level, e.g., within a desired voltage range. As shown by a line 54,
when the switch 32 is closed, current will flow though the battery
16, the relay 12, the inductor 18, the CT 20, the diode 24, the
switch 32, the switch 34, and the relay 14. The current in the
inductor 18 increases when the switch 32 is closed and energy is
stored in the inductor 18. As shown by a line 56, when the switch
32 is open, current will flow through the battery 16, the relay 12,
the inductor 18, the CT 20, the diode 24, the diode 28, the
capacitor 36, the switch 34, and the relay 14. The inductor current
decreases when the switch 32 is open because energy is taken from
the inductor 18 and transferred to the capacitor 36, increasing the
voltage across the capacitor 36, i.e., at the node 50.
During the negative half cycle of the output voltage, the
controller 22 closes the switch 32 and opens and closes the switch
34 as desired. The controller 22 monitors the current through the
CT 20 and the voltage at node 52, determines a PWM rate using the
monitored current and voltage, and opens and closes the switch 34
in accordance with the determined PWM rate to maintain the voltage
at the node 52 at about a desired level, e.g., within a desired
voltage range. As shown by the line 54, when the switch 34 is
closed, current will flow though the battery 16, the relay 12, the
inductor 18, the CT 20, the diode 24, the switch 32, the switch 34,
and the relay 14. The current in the inductor 18 increases when the
switch 34 is closed and energy is stored in the inductor 18. As
shown by a line 58, when the switch 34 is open, current will flow
through the battery 16, the relay 12, the inductor 18, the CT 20,
the diode 24, the switch 32, the capacitor 38, the diode 30, and
the relay 14. The inductor current decreases when, the switch 34 is
open because energy is taken from the inductor 18 and transferred
to the capacitor 38, increasing the voltage across the capacitor
38, i.e., at the node 52.
Operation of the converter 10 in on-battery mode is illustrated in
FIG. 14. As shown, in the positive half cycle of the output
voltage, the switch 34 is conducting and the switch 32 is opened
and closed, yielding a non-zero fluctuating inductor current, a
non-zero fluctuating current through the switch 34, and an
intermittent current through the switch 32. Also as shown, the
current in the switch 32 rises during the time that the switch 32
is closed. In the negative half cycle of the output voltage, the
switch 32 is conducting and the switch 34 is opened and closed,
yielding a non-zero fluctuating inductor current, a non-zero
fluctuating current through the switch 32, and an intermittent
current through the switch 34. As with the switch 32 in the
positive half cycle, the current in the switch 34 rises during the
time that the switch 34 is closed.
Other embodiments are within the scope and spirit of the appended
claims. For example, referring to FIG. 15, a front-end converter 60
includes similar components to the components of the converter 10
shown in FIGS. 11-13. The converter 60, however, further includes a
relay 62, and a controller 64 that is configured to monitor
voltages and currents and control the switches 32, 34 similarly to
the controller 22, but is also coupled to, and configured to
control, the relay 62. The relay 62 is coupled across the diode 24
and configured to selectively bypass the diode 24, with the diode
24 being essentially short circuited when the relay 62 is closed
(conducting). The relay 62 has lower loss than the diode 24, and
may be so low as to be negligible compared to the loss in the diode
24. The controller 64 monitors the mode of the converter 60, i.e.,
whether the converter 60 is in online or on-battery mode. The
controller 64 closes the relay 62 during on-battery mode and opens
the relay 62 during online mode. As current flows through the diode
24 of the converter 10 during both (positive and negative) half
cycles of the output voltage while in on-battery mode, the relay 62
is closed during on-battery mode to reduce energy loss and improve
efficiency by running current through the relay 62 instead of the
diode 24 during on-battery mode of the converter 60.
Three-Phase Circuitry
Referring to FIG. 16, a three-phase, shared-component, front-end
converter 110 is configured to use front-end inductors in an
on-battery mode of operation. Compared to the three-phase front-end
converter 620, the converter 110 has a battery 112 disposed
upstream from a diode bridge 114 as opposed to downstream in the
converter 620, and eliminates the inductor L, thus reducing the
cost of the converter 110 compared to the converter 620. The
converter 110 achieves online UPS front-end converter operation
with only three inductors. The converter 110 is preferably
connected to an inverter as shown in FIG. 1. Thus, an inverter and
an output of the inverter is referred to below although, not shown
in FIG. 16.
The converter 110 includes relays 122, 124, 126, inductors 132,
134, 136, relays 138, 140, CTs 142, 144, switches 146, 148, and
diodes 150, 152. Bus capacitors 154, 156 are disposed between nodes
160, 162 corresponding to positive and negative DC buses,
respectively. The relay 122 is disposed, coupled, and configured to
selectively connect the inductor 132 to either the positive
terminal 113 of the battery 112 or to a first phase input 166 of
the converter 110 corresponding to a first phase output of a source
164. The relay 124 is disposed, coupled, and configured to
selectively connect the inductor 134 to either the negative
terminal 115 of the battery 112 or to a second phase input 168 of
the converter 110 corresponding to a second phase output of the
source 164. The relay 126 is disposed, coupled, and configured to
selectively connect the inductor 136 to, or disconnect/decouple the
inductor 136 from, a third phase input 170 of the converter 110
corresponding to a third phase output of the source 164. Each phase
of the power from the source 164 is connected to the diode bridge
114 through a respective single inductor 132, 134, 136. The battery
112 is connected through the relays 122, 124 and the inductors 132,
134 to provide input power to the rectifying diode bridge 114. The
relay 138 is coupled on one end between the inductor 132 and an
anode of a diode 172 of the bridge 114 and on the other end to a
cathode of the diode 172. The relay 138 is coupled and configured
to selectively bypass and essentially short circuit the diode 172
in response to a signal from a controller 180. The relay 140 is
coupled on one end between the inductor 134 and a cathode of a
diode 174 of the bridge 114 and on the other end to an anode of the
diode 174. The relay 140 is coupled and configured to selectively
bypass and essentially short circuit the diode 174 in response to a
signal from the controller 180.
The controller 180 is coupled and configured to monitor currents
and voltages and controls states of the relays 122, 124, 126, 138,
140. The controller 180 is coupled to the CTs 142, 144 to monitor
currents, is coupled to the inputs 166, 168, 170 to determine
acceptability of input power, is coupled to the output of the
inverter to monitor the output voltage, and is coupled to the
relays 122, 124, 126, 138, 140 to provide control signals to set
the state (open/closed) of the relays 122, 124, 126, 138, 140.
In response to determining that the input power is acceptable, the
controller 180 sets the converter 110 to (or leaves the converter
110 in) the online condition. During online operation, the
controller 180 sets the relays 122, 124, 126 to their NO positions
connecting the source 164 to the inductors 132, 134, 136. Further,
the controller 180 sets the relays 138, 140 to their NC (here open)
positions such that current will flow through the diodes 172, 174
during positive and negative half cycles of the first and second
source phases, respectively. The control of the converter 110
during the AC (online) operation is similar to the online operation
described in U.S. Pat. No. 7,005,759 and the IEEE paper by Xu
referenced above.
In response to determining that the input power is unacceptable,
the controller 180 sets the converter 110 to (or leaves the
converter 110 in) an on-battery mode. The controller 180 sends
signals to the relays 122, 124, 126 to set the relays 122, 124, 126
to their NC positions. In their NC positions, the relays 122, 124
connect the positive and negative terminals of the battery 112 to
the inductors 132, 134, respectively. In its NC position, the relay
126 isolates the inductor 136 from the input 170 and from the
battery 112. Also in response to determining that the input power
is unacceptable, the controller 180 sends signals to set the relays
138, 140 to their NO (here conducting) positions, respectively. In
its NO position, the relay 172 bypasses, essentially short
circuiting, the diode 172 to effectively directly connect the
inductor 132 to the CT 142 with current flowing through the relay
138. In its NO position, the relay 140 bypasses, essentially short
circuiting the diode 174 to effectively directly connect the
inductor 134 to the CT 144 with current flowing through the relay
140.
The controller 180 monitors the output voltage of the inverter, the
voltages at the nodes 160, 162, and the current through the CTs
142, 144, and controls the switches 146, 148 to achieve desired
voltages at the nodes 160, 162. In response to determining that the
output voltage of the inverter is in its positive half cycle, the
controller 180 sends a signal to the switch 148 to close, as shown
in FIG. 16. In response to determining that the output voltage of
the inverter is in, its negative half cycle, the controller 180
sends a signal to the switch 146 to close, as shown, in FIG.
17.
Referring to FIG. 16, during the positive half cycle of the
inverter output voltage, the controller 180 regulates opening and
closing of the switch 146. The controller 180 monitors the current
through the CT 142 and the voltage at node 160, determines a PWM
rate using the monitored current and voltage, and opens and closes
the switch 146 in accordance with the determined PWM rate to
maintain the voltage at the node 160 at about a desired level,
e.g., within a desired voltage range. As shown by a line 182, when
the switch 146 is closed, current will flow through the battery
112, the relay 122, the inductor 132, the relay 138, the CT 142,
the switch 146, the switch 148, the CT 144, the relay 140, and the
inductor 134. The current in the inductors 132, 134 increases when
the switch 146 is closed and energy is stored in the inductors 132,
134. As shown by a line 184, when the switch 146 is open, current
will flow through the battery 112, the relay 122, the inductor 132,
the relay 138, the CT 142, the diode 150, the capacitor 154, the
switch 148, the CT 144, the relay 140, and the inductor 134. With
the switch 146 open, energy is transferred from the battery 112 to
the bus capacitor 154, increasing the voltage across the capacitor
154, i.e., at the node 160.
Referring to FIG. 17, with further reference to FIG. 16, during the
negative half cycle of the inverter output voltage, the controller
180 regulates opening and closing of the switch 148. The controller
180 monitors the current through the CT 144 (and/or the CT 142) and
the voltage at node 162, determines a PWM rate using the monitored
current and voltage, and opens and closes the switch 148 in
accordance with the determined PWM rate to maintain the voltage at
the node 162 at about a desired level, e.g., within a desired
voltage range. As shown by a line 186, when the switch 146 is
closed, current will flow through the battery 112, the relay 122,
the inductor 132, the relay 138, the CT 142, the switch 146, the
switch 148, the CT 144, the relay 140, and the inductor 134. The
current in the inductors 132, 134 increases when the switch 148 is
closed and energy is stored in the inductors 132, 134. As shown by
a line 188, when the switch 148 is open, current will flow through
the battery 112, the relay 122, the inductor 132, the relay 138,
the CT 142, the switch 146, the capacitor 156, the diode 152, the
CT 144, the relay 140, and the inductor 134. With the switch 148
open, energy is transferred from the battery 112 to the bus
capacitor 156, increasing the voltage across the capacitor 156,
i.e., at the node 162. This operation is similar to using twin
boost converters with floating battery as explained above with
reference to single-phase front-end converter operation.
Other embodiments of three-phase converters may be used. For
example, referring to FIG. 18, a converter 210 is configured
similarly to the converter 110 except that two relays 292, 294 are
provided. The relay 292 is connected to the positive terminal of
the battery 112 and selectively connects to a neutral line 296 or
to an open circuit. The relay 294 is connected to the negative
terminal of the battery 112 and selectively connects to the neutral
line 296 or to an open circuit. The switches 292, 294 can be low
voltage FETs rated for battery voltage, e.g., 230V. A controller
280 is configured to control states of the switches 292, 294 in
addition to being configured with much of the functionality of the
controller 180 described above. Operation of the converter 210 in
an online mode is similar to that described in U.S. Pat. No.
7,005,759 and the IEEE paper by Xu referenced above. As with the
converter 110, the converter 210 is preferably connected to an
inverter via the nodes 160, 162, similarly to as shown in FIG. 1,
and thus the inverter and its output are referenced below but not
shown in FIG. 18. The controller 280 monitors the output voltage of
the inverter, the voltages at the nodes 160, 162, and the current
through the CTs 142, 144, and controls the switches 146, 148, 292,
294 to achieve desired voltages at the nodes 160, 162. In response
to determining that the output voltage of the inverter is in its
positive half cycle, the controller 280 sends a signal to the
switch 294 to close, as shown in FIG. 18. As with the switch 148 in
the converter 110, the switch 294 will remain closed during the
positive half cycle. The controller 280 also sends signals to the
switches 292, 148 to open, and these switches will remain open
during the positive half cycle. In response to determining that the
output voltage of the inverter is in its negative half cycle, the
controller 280 sends a signal to the switch 292 to close, as shown
in FIG. 19. As with the switch 146 in the converter 110, the switch
292 will remain closed during the negative half cycle. The
controller 280 also sends signals to the switches 294, 146 to open,
and these switches will remain open during the negative half
cycle.
During the positive half cycle of the inverter output voltage, the
controller 280 regulates opening and closing of the switch 146. The
controller 280 monitors the current through the CT 142 and the
voltage at node 160, determines a PWM rate using the monitored
current and voltage, and opens and closes the switch 146 in
accordance with the determined PWM rate to maintain the voltage at
the node 160 at about a desired level, e.g., within a desired
voltage range. As shown by a line 300, when the switch 146 is
closed, current will flow through the battery 112, the relay 122,
the inductor 132, the relay 138, the CT 142, the switch 146, the
neutral line 296, and the switch 294. The current in the inductor
132 increases when the switch 146 is closed and energy is stored in
the inductor 132. As shown by a line 302, when the switch 146 is
open, current will flow through the battery 112, the relay 122, the
inductor 132, the relay 138, the CT 142, the diode 150, the
capacitor 154, the neutral line 296, and the switch 294. With the
switch 146 open, energy is transferred from the battery 112 to the
bus capacitor 154, increasing the voltage across the capacitor 154,
i.e., at the node 160.
Referring to FIG. 19, during the negative half cycle of the
inverter output voltage, the controller 280 regulates opening and
closing of the switch 148. The controller 280 monitors the current
through the CT 144 and the voltage at node 162, determines a PWM
rate using the monitored current and voltage, and opens and closes
the switch 148 in accordance with the determined PWM rate to
maintain the voltage at the node 162 at about a desired level,
e.g., within a desired voltage range. As shown by a line 304, when
the switch 148 is closed, current will flow through the battery
112, the switch 292, the neutral line 296, the switch 148, the CT
144, the relay 140, the inductor 134, and the relay 124. The
current in the inductor 134 increases when the switch 148 is closed
and energy is stored in the inductor 134. As shown by a line 306,
when the switch 148 is open, current will flow through the battery
112, the switch 292, the neutral line 296, the capacitor 156, the
diode 152, the CT 144, the relay 140, the inductor 134, and the
relay 124. With the switch 148 open, energy is transferred from the
battery 112 to the bus capacitor 156, increasing the voltage across
the capacitor 156, i.e., at the node 162.
* * * * *